Silicones having hydrophilic groups exhibit excellent surface activity due to possessing both a silicone moiety, which exhibits properties such as hydrophobicity, softness, lubricity and chemical stability, and a hydrophilic group moiety, which exhibits properties such as hydrophilicity, moisture retention properties and adhesive properties. Therefore, silicones having hydrophilic groups are widely used in foods, resins, coatings, cosmetic compositions and the like, and a variety of hydrophilic silicone compounds have been known in the past. In particular, silicone oils such as low molecular weight cyclic siloxanes are often blended in order to improve the sensation during use of a cosmetic composition, and polyether-modified silicones (polyether-modified polysiloxanes) are widely used as cosmetic composition raw materials such as surfactants due to exhibiting good compatibility with silicone oils.
In the field of cosmetic products, emulsifiers for water-in-oil emulsions is the use in which the value of polyether-modified silicones is maximized. Water-in-oil emulsion systems exhibit better moisture resistance than oil-in-water emulsions and have the characteristic of being able to maintain an effect such as cosmetic retainability. However, stabilizing water-in-oil emulsions has historically been more difficult than stabilizing oil-in-water emulsions, and until about 30 years ago, the only method for stabilizing water-in-oil emulsions was by solidifying an oil phase (external phase) with a wax (a beeswax-Borax-based emulsifier), which led to poor usability and sensation during use as a cosmetic product. In addition, this technique involved problems such as difficulty in maintaining stability in regions having wide temperature variations and difficulty in adjusting the feeling to touch by altering the oil phase/aqueous phase ratio.
After this, an amino acid gel emulsification method (Non-Patent Document 1) and a high internal phase W/O emulsion using this method were developed in 1977, and a breakthrough was achieved by ameliorating the oily sensation during use by being able to reduce the quantity of the oil phase and gelling the oil phase by means of a lamellar structure obtained by arranging an amino acid and a surfactant in a regular manner, thereby improving the stability of the emulsion. Furthermore, a method for obtaining a stable W/O emulsion by adding an aqueous phase to an oily gel obtained by using a clay mineral that was hydrophobized/oil-swelled by means of a quaternary ammonium salt-based organic cation and the like (Non-Patent Document 2) was developed, and this contributed to broadening the scope of formulations according to the texture and feeling to touch of a water-in-oil emulsion cosmetic composition. However, these conventional W/O emulsion stabilization techniques were developed in order to maintain the stability of a system by gelling or solidifying an oil phase (external phase), meaning that it was difficult to stabilize an emulsion while maintaining a low emulsion viscosity.
With a technique for producing a W/O emulsion having excellent stability while having a low viscosity and good fluidity, it would be possible to obtain a practical W/O emulsion cosmetic composition having a soft feeling to touch, light smoothness and good spreadability. That is, by using this technique in a combination with conventional formulation techniques for obtaining a stable cream, it is possible to freely adjust the texture or feeling to touch of a cosmetic composition according to consumers' wishes and the intended use of the cosmetic composition, and such a composition was thought to be of high value. Therefore, attempts were made to improve the feeling to touch by using the aforementioned techniques in a formulation obtained by adding a silicone oil to an oil phase. However, it is not possible to stably gel a silicone oil by using the aforementioned techniques, and it was not possible to obtain a W/O emulsion cosmetic composition having excellent stability and feeling to touch.
Under such circumstances, attention was focused purely on emulsification performance, not hardening oils, and research into the use of polyether-modified silicones in emulsifiers for water-in-oil emulsions was carried out, mainly in the USA and Europe (Patent Documents 1 to 5). Until around 1985, polyether-modified dimethylpolysiloxanes functioned as useful emulsifiers for oil phases that primarily contain silicone oils, long chain alkyl/polyether-comodified dimethylpolysiloxanes functioned as useful emulsifiers for oil phases that primarily contain organic oils or mixed oils of silicone oils and organic oils, and these were confirmed as having the previously unachievable property of obtaining a W/O emulsion cosmetic composition having both more excellent stability and lower viscosity than previous compositions. <
Thereafter, organic emulsifiers that produced water-in-oil emulsions having low viscosity and excellent stability, such as polyglyceryl polyhydroxystearates and isostearyl glyceryl, were developed, but these materials do not have a silicone moiety in the structure, and therefore have the problem of being unable to obtain a stable emulsion in formulations in which the proportion of a silicone oil in an oil phase is high. In addition, these materials are inferior to polyether-modified silicones in terms of feeling to touch. Therefore, these emulsifiers for organic W/O emulsions are often used in combination with polyether-modified silicones in, for example, formulations in which the proportion of a silicone oil in an oil phase is high.
This is one reason why polyether-modified silicones currently occupy an important position in the field of emulsifiers for water-in-oil emulsions used in cosmetic products.
Meanwhile, glycerin-modified silicones have long been known as non-ionic hydrophilic silicones that differ from polyether-modified silicones (Patent Documents 6 to 19), and investigations into the use of these in cosmetic compositions have increased. However, stable production of glycerin-modified silicones is extremely difficult technically, and unsaturated group-containing glycerin derivatives, which are raw materials of glycerin-modified silicones, are expensive and are difficult to procure on an industrial scale. As a result, the number of commercially available glycerin-modified silicone products is far lower than that of polyether-modified silicones, and because these are also expensive, actual use of glycerin-modified silicones has been limited.
Recently, it has been thought that glycerin-modified silicone was superior to polyether-modified silicone from the perspective of oxidation stability and, thus, glycerin-modified silicone has attracted attention as a surfactant having greater safety. For example, in Germany, a demand for the replacement of raw materials having polyether groups with non-polyether raw materials has increased due to a negative perception of the safety of products comprising polyoxyethylene (PEG) due to testing done by a consumer information magazine company. Moreover, in South Korea, increased interest in non-polyether silicone surfactants has emerged due to a concern that products containing polyoxyethylene (PEG) may irritate the skin because formalin may be produced as a result of oxidation degradation of PEG.
In light of the above, there is a global trend toward changing the entire formulation of end consumer products such as cosmetic products, and the like, to PEG-FREE formulations. In concord with this trend, there is a demand for progression from the old polyether-modified silicone technology to non-polyether hydrophilic silicone in the field of silicone-based surfactants as well. However, as well as being expensive, conventional glycerin-modified silicones have significant problems in that they do not appear in patent document searches. This is because even if glycerin-modified silicone is used as an emulsifier for a water-in-oil emulsion, it cannot be used in an actual formulation because performance is low. As a result, there is no choice but to use a more reliable polyether-modified silicone emulsifier in combination with the glycerin-modified silicone, which makes it impossible to achieve the goal of shifting all cosmetic compositions to PEG-FREE formulations.
More specifically, an undecyl glyceryl ether-modified organopolysiloxane that is disclosed in Patent Document 11 can form a stable W/O emulsion if the oil phase is a silicone oil, but cannot form a stable emulsion in formulations in which an oil phase is a mixed system of an organic oil and a silicone oil or an oil phase primarily contains an organic oil. Therefore, an undecyl glyceryl ether-modified organopolysiloxane cannot be used alone as an emulsifier in this type of formulation, and it is essential for the formulation to be aided by an organic emulsifier or a long chain alkyl/polyether-comodified dimethylpolysiloxane.
In addition, the polyhydric alcohol-modified silicone disclosed in Patent Document 14 is characterized by having a linear siloxane branch as a lipophilic group in the structure, and types having a triglycerin group as a hydrophilic group and a medium chain alkyl group as an optional secondary lipophilic group are commercially available. By having two lipophilic groups in the structure, this material can be used in a wider range of oil agents than the material disclosed in Patent Document 11. Specifically, it is possible to form a stable W/O emulsion with a silicone oil, an ester oil in which the alkyl chain length is not long, a triglyceride, or a mixed oil comprising a silicone oil and a variety of organic oils. However, in cases where the oil phase comprises a non-polar organic oil such as a mineral oil and isododecane or in the case of a mixed oil system in which the proportion of these non-polar oils is high, it is not possible to reduce the emulsion particle diameter due to emulsification performance being poor, particles agglomerate over time or when subjected to heat, and the emulsion separates. As a result, this polyhydric alcohol-modified silicone cannot be used alone as an emulsifier in this type of formulation, and it is essential for the formulation to be aided by an oil-gelling agent such as an organic emulsifier, a long chain alkyl/polyether-comodified dimethylpolysiloxane and a clay mineral that has been hydrophobized/oil-swelled by means of a quaternary ammonium salt-based organic cation and the like.
The branched polyglycerol-modified silicone disclosed in Patent Document 15 is produced by addition/graft polymerizing 2,3-epoxy-1-propanol with a silicone having one or more functional group selected from among the group comprising a hydroxy group, a carboxy group, an amino group, an imino group, a mercapto group and an epoxy group in the presence of an acidic or basic catalyst. However, with this method, the siloxane backbone disconnects during the graft polymerization, which results in two or more components having different properties being prone to be produced as the copolymer. This leads to a multitude of problems related to variable product quality, refining processes, and the like. Therefore, this is an extremely important material for maintaining the stability and emulsion viscosity of an oil-water mixture, that is, a material that is not suited to the functions of an emulsifier. In addition, because branched polyglycerol groups contain an extremely high number of hydroxyl groups per hydrophilic group, when modifying a silicone with the hydrophilic group, the hydrophilic/lipophilic balance (HLB) readily breaks down due to small variations in the degree of modification caused by reaction conditions or raw material considerations, meaning that the stability, viscosity or the like of the W/O emulsion varies greatly according to the branched polyglycerol-modified silicone lot. Therefore, branched polyglycerol groups exhibit an excessively strong autoagglutination force, and therefore tend to significantly increase the viscosity of a branched polyglycerol-modified silicone, meaning that compatibility between an oil phase and a modified silicone is reduced, energy transfer efficiency during mechanical emulsification is reduced, and it is extremely difficult to obtain a stable W/O emulsion having a fine particle diameter.
When explained in relation to the field of cosmetic products, the both terminal silicone-modified glycerin disclosed in Patent Documents 18 and 19 is a material that achieves excellent performance as an agent for dispersing a powder in an oil in cases where the oil phase is a silicone oil, and is a material in which the function as an emulsifier for a water-in-oil emulsion is low both inherently and in terms of being usable with a wide variety of oil agents.
Among Patent Documents 6 to 19, which relate to glycerin-modified silicones, the four technologies mentioned above are used in currently commercially available products. Therefore, it is thought that materials other than these have been judged by the applicant to exhibit insufficient value or effect to be commercialized.
With this in mind, the inventors of the present invention realized the following matters. Applications of monoglycerin-modified silicones, triglycerin-modified silicones and polyglycerin-modified silicones having many glycerin units in cosmetic compositions have been reported in many patent documents, and performance limits of these silicones as emulsifiers for water-in-oil emulsions are clear from market research. However, there has been very little research that focuses on diglycerin-modified silicones (Patent Document 13), and of the many past patent documents that relate to the use of glycerin-modified silicones other than this in cosmetic compositions, only 12 documents disclose diglycerin-modified silicones in practical examples (Patent Document 14 and Patent Documents 20 to 30). Furthermore, only Patent Documents 13 and 26 investigate diglycerin-modified silicones as emulsifiers for water-in-oil emulsions.
More specifically, in Patent Document 14, the siloxane compound 1 in the practical examples corresponds to a diglycerin-modified silicone, but only the detergent composition in Practical Example 1, the make-up remover in Practical Example 8 and the make-up remover in Practical Example 11 relate to the blending of this siloxane compound 1 in a cosmetic composition, and all three are aqueous systems that do not contain an oil component. Therefore, these documents do not investigate the use of diglycerin-modified silicones as emulsifiers for water-in-oil emulsions.
Patent Documents 20 to 24, 28 and 29 are formulations that are completely different from water-in-oil emulsions, and therefore do not mention investigations into the use of diglycerin-modified silicones in this type of use. Patent Document 25 relates to a method for refining a modified silicone compound having a branched polymer comprising a hydrophilic group, and only discloses a method for producing a deodorized diglycerin-modified silicone in Practical Example 5 and preparing a non-aqueous oil-based foundation using this deodorized diglycerin-modified silicone in Practical Example 14. Therefore, these documents do not investigate the use of diglycerin-modified silicones as emulsifiers for water-in-oil emulsions. In addition, Patent Document 30 discloses a technique for providing a cosmetic composition containing a silicone oil-containing oil agent and having excellent emulsion stability, but only discloses a diglycerin-modified silicone in Synthesis Example 5, and does not disclose a practical example in which this diglycerin-modified silicone is actually blended in a cosmetic composition.
Patent Document 26 relates to a cosmetic composition that is characterized by containing a clay mineral and the polyhydric alcohol-modified silicone disclosed in Patent Document 14, and Production Example 6 discloses a diglycerin-modified silicone having a specific structure. In addition, Practical Example 14 discloses a water-in-oil cream that contains this diglycerin-modified, silicone and dimethyldistearyl ammonium hectorite. However, because the viscosity of the emulsion is too low when the diglycerin-modified silicone of Production Example 6 is used as an emulsifier, stability cannot be maintained unless the oil phase is thickened by means of the clay mineral. In addition, this diglycerin-modified silicone has poor compatibility with a variety of organic oils, and even if the clay mineral is additionally used in a formulation in which the proportion of an organic oil in the oil phase is high, the stability of the emulsion cannot be maintained.
Patent Document 27 is an invention that relates to a powder composition and powder-in-oil dispersion comprising a powder and/or a coloring agent and, of the polyhydric alcohol-modified silicones disclosed in Patent Document 14, a polyglycerin-modified silicone having a linear siloxane branch, and also relates to a cosmetic composition containing these, and Production Example 1 discloses a diglycerin-modified silicone having a specific structure. Practical Example 1 discloses a powder-in-oil dispersion, Practical Example 5 discloses a powder composition, Practical Examples 9 and 13 disclose sunscreen agents, Practical Example 17 discloses an oil-in-water cream, Practical Example 21 discloses a water-in-oil cream, Practical Example 23 discloses a foundation, Practical Example 29 discloses an eye liner, Practical Examples 37 and 38 disclose a sun-screening milky lotion, Practical Example 40 discloses an O/W sun-screening milky lotion, and these contain this diglycerin-modified silicone. However, in all of these water-in-oil emulsion-based formulations (Practical Examples 9, 13, 21, 23, 29, 37 and 38), the diglycerin-modified silicone is used as a powder dispersing agent or an agent for treating the surface of a powder, and a polyether-modified silicone and/or a crosslinked polyether-modified silicone is used as an emulsifier for a water-in-oil emulsion in all of these examples. Therefore, these documents do not investigate the use of diglycerin-modified silicones as emulsifiers for water-in-oil emulsions. Furthermore, this diglycerin-modified silicone has poor compatibility with a variety of organic oils, and it is not possible to obtain a stable powder-in-oil dispersion in a formulation in which the proportion of an organic oil in the oil phase is high.
Patent Document 13 discloses a glyceryl ether-modified organo(poly)siloxane having a specific structure, a method for producing same, and a cosmetic composition containing the same, and Practical Examples 2, 4, 6 and 8 disclose compounds corresponding to diglycerin-modified silicones and methods for producing same. In addition, the results of an emulsification test (water-in-oil emulsion) of a simple formulation comprising the compound of Practical Example 2, a silicone oil and water are reported in Experimental Example 1, and the results obtained by blending the compound of Practical Example 2 in a hair rinse (aqueous system) having a specific composition are reported in Cosmetic Composition Formulation Example 1. However, the diglycerin-modified silicones disclosed in Practical Examples 2, 4, 6 and 8 exhibit poor compatibility with a variety of organic oils, and it is not possible to obtain a stable W/O emulsion in a formulation in which the proportion of an organic oil in the oil phase is high, meaning that separation occurs over time or when subjected to heat. Therefore, an undecyl glyceryl ether-modified organopolysiloxane cannot be used alone as an emulsifier in this type of formulation, and it is essential for the formulation to be aided by an organic emulsifier or a long chain alkyl/polyether-comodified dimethylpolysiloxane.
In Patent Document 31, the applicant of the present application proposes the use of a co-modified organopolysiloxane copolymer having a group that has a carbosiloxane dendron structure and a hydrophilic group such as glycerin and a polyhydric alcohol in the molecule as a surfactant, powder treatment agent or surface treatment agent able to be advantageously used in the field of cosmetic compositions. In practical example 13 in particular, the applicant of the present application proposes a novel glycerin derivative-modified silicone (No. 13) having a group that has a siloxane dendron structure, a tetraglycerin derivative group and a diglycerin derivative, and also proposes a water-in-oil emulsion composition containing these (Formulation Example 5) and a W/O emulsion type skin external use preparation (Formulation Example 33). The glycerin derivative-modified silicone proposed here can be used to prepare a stable water-in-oil emulsion when the oil phase is a mixed system of a silicone oil and an organic oil or an oil phase primarily contains an organic oil, and has excellent feeling to touch as a cosmetic composition, but emulsification per se is difficult in a system in which a non-polar organic oil having a relatively high molecular weight, such as a mineral oil, is the primary component of the oil phase, and the emulsion stability, and especially long term emulsion stability at high temperatures, of this system has room for improvement.
As aforementioned, regarding diglycerin-modified silicone, there have been only a few reported cases of application review of emulsifiers for water-in-oil emulsions, and to date only a few with limited structures have been tested. In addition, when compared with ordinary polyether-modified silicones (polyether-based hydrophilic silicone emulsifiers), no glycerin-modified silicones having sufficient emulsification performance with a wide range of oil agents are known as emulsifiers for water-in-oil emulsions. As a result, glycerin-modified silicones, which have a better feeling to touch than polyether-modified silicones and which do not suffer from oxidative degradation due to not having a polyoxyethylene (PEG) structure, could not produce a water-in-oil emulsion cosmetic composition having sufficient stability without additionally using a non-ionic surfactant such as another hydrophilic silicone emulsifier having a PEG structure, and could not achieve the objectives of sufficiently exhibiting a feeling to touch improvement effect as an overall formulation and improving a cosmetic composition to a completely PEG-FREE formulation (a formulation that does not contain a compound having a polyoxyethylene (PEG) structure).